Effect of minor additions on structure and volatilization loss in simulated nuclear borosilicate glasses

Structural and thermal properties are reported for a range of caesium oxide-containing alkali borosilicate glasses, of the form xCs2O(100 − x)ZMW (0 < x < 10), where ZMW represents a variety of simulated base-glasses. Glass densities increase and glass transition temperatures decrease with increase in caesium oxide concentration. Mass-loss from the melt is found to depend on composition in the same manner as the fraction of silicon Q3 units, resolved from 29Si MAS NMR, and is related to the presence of danburite medium-range order units, resolved from 11B MAS NMR. Volatilization is shown to occur even in the absence of caesium oxide and the mixed alkali borosilicate composition of the volatile species, evolved from the melt at high temperature, is independent of the starting composition of the glass.